This invention relates generally to the field of pneumatic actuators and, more particularly, to a canister employing a closely fitting end cup receiving the canister body housing the actuator.
Pneumatic actuators are used for various duties where relatively high reaction speed, simple devices are needed for linear or cable actuation. One such use has been the control of wastegates and variable nozzle devices for turbochargers. Numerous designs exist for such actuators including those disclosed in U.S. Pat. No. 4,893,474 TURBOCHARGER WITH DUAL FUNCTION ACTUATOR, U.S. Pat. No. 5,172,552 TURBOCHARGER WITH FLEXIBLE CABLE WASTEGATE OPERATING LINKAGE, U.S. Pat. No. 5,487,273 TURBOCHARGER HAVING PNEUMATIC ACTUATOR WITH PILOT VALVE, U.S. Pat. No. 5,746,058 ADJUSTABLE ACTUATOR FOR A TURBOCHARGER, U.S. Pat. No. 5,787,591 TURBOCHARGER ACTUATOR WITH ROLLING O-RING, U.S. Pat. No. 6,155,048 ACTUATOR FOR A TURBOCHARGER.
A typical configuration for a prior art actuator is shown in FIG. 1. The actuator has a canister 10 having a cylindrical body 12 and an end wall 14. A spring 16 engaging a piston 18 which is covered by and/or attached to a diaphragm 20 to linearly position a rod 22 to provide the actuating mechanism. The actuator canister incorporates a end cap 24 which includes a fitting 26 for attachment of the pneumatic source. The end cap is crimped to the canister body in a joint 28 which also constrains and seals the peripheral circumference of the diaphragm. The spring is constrained opposite the piston by a spring plate 30. The end wall of the canister is strengthened with a plate 32 inserted between the end wall and spring plate. The spring plate also constrains the seal 34 surrounding the rod.
Attachment of the canister to a bracket or other mounting means is accomplished using studs 36 which are held in a mounting plate 38. The mounting plate is welded to the end wall, either with a continuous circumference weld or with spot or projection welds. In operation, the actuator is subjected to significant cyclical loads which result in a high risk of fatigue in the weld or canister wall resulting in cracking and failure of the actuator.
It is, therefore, desirable to have an actuator canister which eliminates the required welding of a mounting plate to the end wall, both for elimination of the fatigue cracking failure mode and as a cost reduction by elimination of the welding requirement.
A pneumatic actuator containing the present invention incorporates a canister body having a substantially cylindrical side wall and an end wall. The end wall has multiple apertures arranged around a central aperture. A spring engages a piston which is attached to a diaphragm and to an actuating rod for pneumatic actuation. The diaphragm is attached to the canister wall for the pneumatic seal and the rod extends through the central aperture.
A cup is sized to closely receive an end portion including the end wall of the canister body. The cup has matching apertures aligned with the apertures in the end wall and a second central aperture through which the rod extends. An end plate is inserted within the canister body and abuts the end wall. The end plate also has apertures aligned with the apertures in the end wall and a central aperture through which the rod extends. Attachment studs having a shank and head provide the means to attach the actuator to a bracket or other support device. The shank of each stud is inserted through one of the multiple apertures in the end plate, end wall and cup and the head engages the end plate.
A spring plate including a substantially circular face engages the heads of the studs to urge the studs against the end plate. An outer cylindrical upset portion of the spring plate engages the spring at a second end and an inner cylindrical portion having a flange extending radially inwardly distal from the face constrains a seal for the rod. The seal rests against the end plate around the central aperture. The inner cylindrical portion of the spring plate constrains the seal radially and the spring plate flange constraining the seal axially in cooperation with the end plate. A standard fitting in the canister end opposite the cup provides a means for supplying pneumatic pressure to the diaphragm.